The synthesis of amphiphilic polymers, i.e., polymers that combine hydrophilic and hydrophobic moieties, has recently grown in interest to contemporary researchers for a variety of scientific and practical reasons.
The synthesis of block ionomers has gained interest and importance in a number of industries. Early work with DMAEMA is found in Kennedy, U.S. Pat. No. 4,942,204, and Ivan, et al., U.S. Pat. No. 5,073,381, both of which disclose free radical polymerization of methacryloyl endcapped polyisobutylene (MA-PIB-MA) with DMAEMA or hydroxyethyl methylmethacrylate (HEMA). The product of these inventions is a random amphiphilic network, capable of swelling with and absorbing up to about 170% of its weight in either a polar or non polar solvent, while remaining insoluble in either. Control of overall network molecular weight and concentration of one constituent within the copolymer network are significant parameters of this invention. The networks disclosed therein are intended to perform timed release of pharmaceuticals in vivo.
Matyjaszewski, U.S. Pat. No. 5,763,948 teaches atom transfer radical polymerization (ATRP) as a method of synthesizing low polydispersity (Mw/Mn) block copolymers via anionic polymerization. Such control over polydispersity is obtained through use of a transition metal catalyst which acts as a carrier of a halogen atom in a redox process. As the reaction proceeds, the molecular weight distribution of the copolymer product decreases, approaching 1.10. Typical monomers to be polymerized via ATRP include methacrylates, styrenes and dienes. However, this patent does not disclose the ionization of a methacrylate or amine after ATRP addition to a hydrophobic block. Further, this patent discloses that inasmuch as ATRP is radical polymerization, blocks can be prepared in essentially any order.
U.S. Pat. No. 6,069,205, to Wang, a former student of Professor Matyjaszewski, discloses polymerization of an ethylenically unsaturated monomer and a cationically polymerizable monomer through the ATRP process to form diblock or triblock copolymers. Many of the suitable unsaturated monomers are highly polar, such as 2-hydroxyethyl methacrylate. One stage in this polymerization is the conversion of terminal halogen atoms to hydroxyl or metal salts. The resultant copolymers of this invention have low polydispersities, in the range Mw/Mn=1.30 to 1.74.
Professor Matyjaszewski's latest ATRP method is disclosed in U.S. Pat. No. 6,162,882, which teaches processes for synthesizing homopolymers, graft copolymers or block copolymers of general type ABA wherein A is at least monofunctionalized and B is at least bifunctionalized. At least one of B's functional groups is a radically transferable atom or group. The improvement thereof over previous ATRP technology is the ability to polymerize polar monomers. As with previous ATRP work, molecular weight and polydispersity control are key objects of this invention; polydispersities as low as 1.04 are disclosed. Disclosed therein is a reaction scheme for the production of a block copolymer having methyl-methacrylate monomers and isobutylene monomers. Block copolymers having a polyisobutylene block also are possible. However, as thermoplastic polymers born of this method have blocks which are thermodynamically incompatible, such polymers exhibit two glass transition temperatures.
Building on prior work at the University of Akron, Kennedy, et al., U.S. Pat. No. 6,200,589, disclose semipermeable amphiphilic membranes capable of immunoisolation. This capability, which is manifest as selective permeability, and depends on the size of the target molecule, is necessary for the intended application. An exemplary application is an implant for long-term use as a reservoir for foreign cells performing a therapeutic function, such as the maintenance of transplanted islet of Langerhans cells releasing insulin in the treatment of Type I diabetes. The implant device contains both hydrophobic segments (radicalized polyolefins) and hydrophilic segments (polyacrylates).
Neither the scientific nor the patent literature contains any mention of block copolymers having a saturated rubber block and an ionomeric block, nor the quaternization or hydrolysis of such an ionomeric block.
It would be advantageous then, to provide a block ionomer having a saturated rubber block and an ionic block. Similarly, it would be advantageous to provide a method for synthesizing a block ionomer.